Composite boards comprising cellulosic plant material

ABSTRACT

There is described a composite board comprising: iv) cellulosic plant material; v) a hydrophilic substance; and vi) an adhesive or resin. There is described a method of making a composite board comprising the steps of: i) providing particulate cellulosic plant material; ii) treating the cellulosic plant material with a hydrophilic substance; iii) adding an adhesive or resin to the cellulosic plant material treated with the hydrophilic substance iv) forming a board with the mixture formed in step iii); and v) drying the board.

FIELD OF THE INVENTION

The present invention relates to composite boards such as particle and fibre boards that comprise cellulosic plant material derived from woody plants and non-wood plants and mixtures thereof. Methods of making the composite boards are also provided.

BACKGROUND OF THE INVENTION

Standard wood based particle and fibre boards are commonly used building materials. However, the wood used to make particle and fibre boards, typically comes from trees, such as Pinus radiata. Such trees take years of cultivation before they can be harvested for use and plantation operations require large investment in land and running costs such as machinery and transport. Furthermore, often branches and bark are discarded and not, used in the manufacture of particle board because of their high mineral content.

Blends of virgin wood and recycled wood reduce the cost of manufacture of particle boards. However, recycled wood has often been treated with chemicals such as stains or preservatives which make them more difficult to use in the manufacture of particle boards. Different species of wood also include varying amounts of organic compounds such as lipids, alkaloids, waxes, proteins, phenolics, sugars, pectins, mucilages, gums, resins, terpenes, starches, glycosides, saponins and essential oils and inorganic compounds such as silicates, phosphates, carbonates, sulfates and oxalates. These compounds may affect the amount of resin required and also other optional additives, such as waxes, when manufacturing the particle board.

In recent years, particle and fibre boards have been made with other sources of cellulose fibre, such as agricultural biomass including corn stover, rice straw, wheat straw, switch grass, and sugar cane bagasse. However, many of these particle and fibre boards require the use of expensive resins and do not meet the required standard for use in structural applications in construction. They also often are not suitable for applications where nails or screws are required.

There is a need for particle and fibre boards that are made from less expensive wood derived cellulosic material and/or cellulosic material that is from readily available, fast growing cellulose sources or from agricultural waste materials that are inexpensive to produce and meet the required standards for structural applications in construction.

SUMMARY OF THE INVENTION

The present invention is predicated in part on the discovery that cellulose plant material treated with a hydrophilic substance may be used to produce particle and fibre boards that meet Australian Standards for structural use in construction and are suitable for use with fixing methods using nails and screws.

DESCRIPTION OF THE INVENTION

In one aspect of the invention, there is provided a composite board comprising:

-   -   i) cellulosic plant material;     -   ii) a hydrophilic substance; and     -   iii) an adhesive or resin.

In some embodiments, the composite board is a particle board or fibre board such as medium-density fibre board or high-density fibre board.

The cellulosic plant material is obtained from woody plants such as trees, recovered or recycled wood or may be non-wood cellulosic plant material, or mixtures thereof. In some embodiments, the cellulosic plant material is derived from woody plants. In some embodiments the cellulosic plant material is derived from recovered or recycled wood. In some embodiments, the cellulosic plant material is non-wood cellulosic plant material. In some embodiments, the cellulosic plant material comprises two or more of cellulosic plant material derived from at least one woody plant, cellulosic material derived from recovered or recycled wood and non-wood cellulosic plant material.

Cellulosic plant material derived from a woody plant may be any type of wood fibres or chip that are currently used in the manufacture of composite boards. The wood fibres or chip may be hardwood or softwood and may be influenced by the availability and type of wood that is obtained from locally grown trees. The wood fibre or chip may be obtained from trees grown to produce wood fibre or chip or may be obtained as sawdust or offcuts of wood formed during processing of logs or the manufacture of wood products, such as furniture. In some embodiments, the cellulosic plant material may comprise wood chip or fibre derived from tree branches and/or bark.

Suitable wood used to provide the cellulosic plant material is derived from trees including coniferous species such as pine, far, spruce or hemlock; or hardwood species such as oak, cherry, poplar, maple, larch, aspen, alder, gum, hickory, birch and beech.

Cellulosic plant material derived from recovered or recycled wood may be derived from any waste wood originally used in a different product, for example, fence palings, telephone poles or lamp posts, weatherboards, pallets, discarded furniture or waste or discarded particle boards or may be from construction or demolition sites. The recovered or recycled wood may have been treated to prevent attack by pests such as fungi or termites, or may have a surface treatment such as a stain, lacquer or paint. Recovered or recycled wood may be from woods such as pine, fir, ash, hickory, beech, birch, cedar, redwood, hemlock, spruce, oak, maple, cherry, walnut, rosewood, teak and the like.

As used herein, the term “non-wood cellulosic plant material” refers to plant material that contains cellulose fibres and that is derived from a plant source other than a tree. The non-wood cellulosic plant material may be agricultural plant material or may be derived from unwanted plants such as weeds. Agricultural plant material may be plant material derived from crop waste, where the plant material is a waste product produced when harvesting a crop. Agricultural plant material also includes cellulosic plant material grown specifically for the production of cellulosic material. In particular embodiments, the plants grown specifically for production of cellulosic material are from plants that are fast growing, for example those that may be harvested at least once a year, such as once a year, twice a year, or three times every two years. In other particular embodiments, the non-wood cellulosic plant material is derived from agricultural crop waste.

Suitable non-wood cellulosic plant material includes cereal straws such as corn stover, rice straw, wheat straw, barley straw, oat straw and rape seed straw, non-edible grasses such as switch grass and siteria grass, flax, yukka fibre, lemongrass, jute, sisal, bamboo, pine needles, lupins, kenaf, coir fibre, coconut husks, cotton stalks, coffee husks, ground nut husks, areca nut husks, casaurina leaves, banana leaves and banana stem. In some embodiments, the non-wood cellulosic material is not lemongrass, particularly when used as the sole source of cellulosic material.

In some embodiments, where the cellulosic plant material is derived from a blend of wood fibre or chip, material derived from recycled or recovered wood, and/or non-wood cellulosic plant material, the virgin wood chip or fibre is present in an amount of 1% to 99%, especially 10 to 90%, 20 to 80%, 30 to 70% or 40 to 60% of the cellulosic plant material. In some embodiments, the virgin wood fibre or chip is present in the cellulosic plant material at about 50% or less. The remainder of the cellulosic plant material is derived from wood fibre or chip from recovered or recycled wood, non-wood cellulosic plant material or a mixture thereof.

The particle size of the cellulosic plant material is any size suitable to make composite boards. In general, the average particle size of the cellulosic plant material is in the range of 5 to 200 mm in length, especially 10 to 150 mm in length or 10 to 100 mm in length. The average width of the particles is generally between 0.2 and 5 mm, especially 0.2 and 1 mm or 0.2 to 0.5 mm.

As used herein, the term “hydrophilic substance” refers to a compound or composition that is able to interact with the plant material surface and increase the hydrophilicity of the plant material surface. Suitable hydrophilic substances include polyhydroxy compounds, polycarboxylic acids, hydroxycarboxylic acids, amino acids and hydroxyamino compounds. Suitable hydrophilic substances include, but are not limited to, ascorbic acid, citric acid, tartaric acid, succinic acid, adipic acid, glutaric acid, glycerine and carbohydrates such as glyceraldehyde, erythrose, threose, ribose, arabinose, xylose, lyxose, allose, alrose, glucose, mannose, gulose, idose, galactose, talose, sucrose, maltose, lactose, fructose or mixtures thereof. In a particular embodiment, the hydrophilic substance is ascorbic acid. In some embodiments, the hydrophilic substance is sucrose.

The hydrophilic substance may be in any form suitable for coating the surface of the cellulosic plant material. In particular embodiments, the hydrophilic substance is in crystalline form or powdered form or powdered crystalline form.

The hydrophilic substance is present in an amount suitable to coat the cellulosic plant material and may depend on the type of cellulosic plant material used. For example, the hydrophilic substance may be present in an amount of about 1 to 50% by weight of the cellulosic plant material. In particular embodiments, the hydrophilic substance is present in an amount of about 1 to 25% by weight of the cellulosic plant material, especially 1 to 15% by weight or 1 to 10% by weight, more especially 3 to 8% by weight or 3 to 7% by weight, most especially 3 to 5% by weight. In some embodiments, the hydrophilic substance is present in an amount of 3.5 to 6% by weight of the cellulosic plant material.

The adhesive resin may be any conventional adhesive or resin used in making standard wood particle or fibre boards. The adhesive may be a thermosetting or thermoplastic polymer. Suitable resins and adhesives include melamine, aldehyde, urea, isocyanate, phenolic, resorcinolic and epoxy resins and polyvinylacetate adhesives.

In some embodiments, the resin is selected from a formaldehyde resin, a urea melamine resin, a melamine formaldehyde resin, a phenol formaldehyde resin, a phenol melamine formaldehyde resin, a melamine resin, a urea formaldehyde resin, a melamine urea formaldehyde resin, a melamine urea phenolic formaldehyde resin, a methylene diphenyl diisocyanate resin, a polymethylene diphenyl diisocyanate (MDI or pMDI, such as polymethylenediphenyl-4,4′-diisocyanate) resin or a combination thereof. The adhesive may especially be a formaldehyde resin, a urea melamine resin, a melamine formaldehyde resin, a melamine resin, a urea formaldehyde resin, a melamine urea formaldehyde resin, a melamine urea phenolic formaldehyde resin, a methylene diphenyl diisocyanate resin, a polymethylene diphenyl diisocyanate (such as plymethylenediphenyl-4,4′-diisocyanate) resin, or a combination thereof. In a particular embodiment, the resin is a melamine urea formaldehyde resin. In other embodiments, where a formaldehyde-free product is desired, the resin is a methylene diphenyl diisocyanate resin.

The amount of adhesive or resin used will depend on the nature of the adhesive or resin but in general will be in the range of 1 to 40% by weight. In some embodiments, where the adhesive is a polyvinylacetate adhesive, the adhesive may be present in an amount of 20 to 40% by weight of the cellulosic plant material. In other embodiments, where the resin is a formaldehyde containing resin, the resin maybe present in an amount of 10 to 20% by weight of the cellulosic plant material. In yet other embodiments, where the resin is a diisocyanate resin, the resin is present in an amount of 1 to 10% by weight of the cellulosic plant material.

The particle or fibre board may also optionally include other additives such as waxes, dyes, hardeners, finishing agents, fire retardants, release agents, plasticisers, fillers, biocides pigments, catalysts, formaldehyde scavengers, ultraviolet light absorbers or combinations thereof. Some of these additives may be included in the resin or adhesive composition.

Waxes may be present to impart water resistance of the finished product. Suitable waxes include paraffin wax and bees wax. Waxes may be present in an amount of 0.1 to 2%, especially 0.5 to 1% by weight of the cellulosic plant material.

Suitable hardeners include ammonium chloride, ammonium sulphate and magnesium chloride. Hardeners may be present in an amount of from 1 to 5%, especially 1 to 4% by weight of the cellulosic plant material.

Suitable fire retardants include boric acids zinc borate, magnesium hydroxide, borax or combinations thereof. Suitable amounts of fire retardant may be between 0.1 and 10% by weight of the adhesive or resin.

Suitable release agents include organic phosphates, thiophosphates, pyrophosphates and other organic phosphate compounds. Suitable biocides include zinc borate, copper ammonium acetate, copper ammonium carbonate, copper betaine compounds and the like. A suitable UV absorber is titanium dioxide. Dyes and pigments may be incorporated into the particle board or fibre board to provide a desired colour finish. Amounts of dyes and pigments incorporated may be any amount suitable to obtain the desired colour finish. A suitable formaldehyde scavenger is melamine. These components may be optionally included in the composite boards in amounts as known in the art for standard or conventional composite boards.

In some embodiments, silica, silicates, biochar, wood char and ash may be added to the cellulosic plant material during the manufacture of the composite board, in amounts of between 0.1 to 10% by weight of the cellulosic plant material. Without wishing to be bound by theory, biochar and wood char are being considered as potential products that could be used for sequestration of carbon. Incorporation of such products into the particle board is also a means of sequestering carbon.

The outer surface of the particle or fibre board may further include a vaneer, such as a wood vaneer or plastic vaneer. Suitable plastic vaneers include melamine and polyvinyl chloride laminates.

In another aspect of the invention there is provided a method of making a composite board as described above comprising the steps of:

-   -   i) providing particulate cellulosic plant material;     -   ii) treating the particulate cellulosic plant material with a         hydrophilic substance;     -   iii) adding an adhesive or resin to the particulate cellulosic         plant material treated with the hydrophilic substance and         mixing;     -   iv) forming a board with the mixture from step iii), and drying         the board.

In some embodiments, the composite board is a particle board or fibre board such as medium-density or high-density fibre board.

The cellulosic plant material is of a size suitable to make composite board. In general, the average particle size of the cellulosic plant material is in the range of 5 to 200 mm, and will depend on the type of the cellulosic plant material used. In some embodiments, the average particle size is in the range of 5 min to 150 mm, 10 mm to 150 mm, 10 mm to 100 mm, especially 20 mm to 80 mm in length. Typically the particles have a width of between about 0.2 and 5 mm, especially 0.2 and 1 mm, more especially 0.2 and 0.5 mm.

The cellulosic plant material particles may be prepared by standard means in the art such as mulching, chopping, flaking, chipping and milling. Such processes may be repeated until a suitable average particle size has been obtained. In embodiments where precise particle dimensions are less important, hammer-milling or disc-chipping may be suitable to produce the particles of cellulosic plant material. In embodiments where precise particle sizes are required, disc-flaking or knife-ring flaking may be used. In some embodiments, the particles may be sieved or sorted by airflow separation to remove larger or smaller undesirable particles or to provide particles with a maximum or minimum size limit.

In some embodiments, the cellulosic plant material is dried prior to milling, mulching, chipping, flaking or chopping. Drying may be achieved in sunlight and low humidity or in an oven. In some embodiments, the cellulosic plant material is dried to a moisture content or about 13 to 15% prior to particle formation. In some embodiments, the cellulosic plant material particles obtained from milling, chopping, chipping, flaking or mulching are dried, optionally in a kiln to provide a moisture content of 2% to 8% by weight, especially about 3% by weight. In some embodiments, the hydrophilic substance is added after particle formation but before drying. In other embodiments, the hydrophilic substance is added after particle formation and after drying.

The particles of cellulosic plant material are treated with the hydrophilic substance before adding the adhesive or resin.

The treatment with the hydrophilic substance may occur in any manner that allows the hydrophilic substance to come into intimate contact with the surface of the non-wood cellulosic plant material, for example, by spraying or dusting. The hydrophilic substance may be a liquid or a solid; for example, a powder, a crystalline form or a powdered crystalline form. In particular embodiments, the hydrophilic substance is a powder or powdered crystalline form.

The resin or adhesive may be added and blended with the cellulosic plant material in any suitable manner. For example, the particulate cellulosic plant material coated with hydrophilic substance may be placed in a blender and stirred while liquid resin is poured or sprayed onto the cellulosic material.

In some embodiments, the adhesive or resin composition comprises at least one additive selected from waxes, dyes, hardeners, finishing agents, fire retardants, release agents, plasticisers, fillers, biocides, pigments, catalysts, formaldehyde scavengers and ultraviolet light absorbers, especially waxes and hardeners. In some embodiments, one or more of these additives is included in the adhesive or resin composition. In some embodiments, one or more of these additives is added to the plant material before addition of the resin.

In some embodiments, silica, silicates, biochar, wood char or ash may be added to the cellulosic plant material, especially after particle formation and/or particle size separation. The amount of silica, silicates, biochar, wood char or ash may be in the range of 0.1 to 10% by weight of the cellulosic plant material. In some embodiments, the silica, silicates, biochar, wood char or ash may be added to the resin or adhesive.

After addition of the adhesive or resin, the composite board is prepared in the same manner as conventional particle or fibre boards. The cellulosic plant material, hydrophilic substance and adhesive or resin mixture is formed into a mat and treated by hot-pressing to activate the resin bonding the cellulosic material together. The temperature used is generally above 100° C., for example between 140° C. and 185° C. The pressure is usually between 2 and 7 MPa, especially about 4.5 MPa. After pressing, the boards are cooled.

Optionally a veneer finish may be applied.

Optionally the composite boards may be finished by trimming and/or sanding to give an appropriate or desired size and finished surface.

Throughout the specification and the claims which follow, unless the context requires otherwise, the word “comprise”, and variations such as “comprises” and “comprising”, will be understood to imply the inclusion of a stated integer or step or group of integers of steps but not the exclusion of any other integer or step or group of integers or steps. As used herein, the term “about” refers to a quantity, level, value, dimension, size, or amount that varies by as much as 30%, 25%, 20%, 15% or 10% to a reference quantity, level, value, dimension, size, or amount.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 illustrates diagrammatically the process of one or more of the following examples to the production of a multi-layered board.

FIG. 2 illustrates diagrammatically the process of one or more of the following examples to the production of a single-layered board.

The invention will now be described with reference to the following Example which illustrates some aspects of the present invention. However, it is to be understood that the particularity of the following Example is not to supersede the generality of the preceding description of the invention.

Example 1 Non-Wood Cellulosic Material Particle Board

Non-wood cellulosic plant material was dried in ambient conditions of humidity and sunlight for 3 to 5 days. Once dry, the plant material was mulched. Mulching was repeated until the average particle size was 60 mm.

The plant material was dusted with ascorbic acid, 3.5-4% by weight of the plant material being treated. Following this treatment, the plant material was dried in a kiln to provide a moisture content of below 3%.

Particle boards were prepared to 16 mm thickness using standard techniques with the following components:

-   -   1. Ascorbic acid treated plant material     -   2. 15% by weight melamine urea formaldehyde resin     -   3. 0.7% by weight wax     -   4. 3% by weight of ammonium sulphate.

The product particle boards were formed into a mat and hot-pressed.

The product particle boards were tested to Australian standards AS4266.5 (bending strength, MOR), AS4266.5 (modulus of elasticity, MOE), AS4266.6 (internal bond), AS4266.8 (24 hour thickness swelling) and AS4266.10 (wet bonding strength, MOR-A).

The particle board products met the Australian Standards as shown in Table 1:

TABLE 1 Standard Australian Standard Sample Result Internal Bond 300 KPa 508 KPa Elasticity —   2732 MPa  Bend Strength >12 MPa   15 MPa 24 Hr Thickness Swell  <15% 8.6% Wet bonding strength >4.5 MPa  5.0 MPa

Example 2 Particle Board Made with Cellulosic Plant Material Derived from Wood Blend

A mixture of wood derived cellulosic materials in the form of sawdust comprising hardwood (ironbark and camphor) and softwood (pine shavings from Pinus radiata) were sieved to remove particles less than 5 mm in length. The average particle size of the sawdust was 5 mm to 60 mm in length for the hardwood sawdust and 5 mm to 40 mm in length for the softwood sawdust.

An aluminium tray (210 mm×270 nm) was lined with aluminium foil and an oven was preheated to 100° C.

105 g of the cellulosic material was dusted with 4 g (3.5%) of powdered crystalline ascorbic acid. It was not clear visually that good even coverage of the cellulosic material was achieved so a further 4 g of ascorbic acid was added. Coverage of the cellulosic material was tested by exposing a sample of the coated material to a flame and observing the ascorbic acid turn golden brown. Even coverage was confirmed.

200 g of polyvinylacetate (PVA) glue was added and the mixture blended and placed in the aluminium tray. The mixture was baked at 100° C. for 30 minutes. the board was removed from the oven, wrapped in plastic wrap (Gladwrap®) and placed between two pieces of medium density particle board. Pressure was applied by placing the boards under the front wheel of a 2400 kg vehicle for 10 minutes. The plastic wrap was removed and the board was reheated at 100° C. for 10 minutes after which pressure was applied again. This heating and pressure process was repeated once more, then the board was allowed to cool. The board produced looked like and had the properties of standard particle board.

Example 3 Particle Board Made from Wood Cellulosic Material

The process described in Example 2 was repeated with 40 g pine shavings (5 mm-40 mm in length) and 18 g of icing sugar. The icing sugar comprised not only sucrose but also tapioca starch (2-4% w/w) to improve flowability of the icing sugar. The board produced was a clean looking particle board that was light in weight due to the low density of the pine shavings.

Example 4 Blend of Wood and Non-Wood Cellulosic Material

20 g of a 50:50 blend of pine shavings and cellulosic material derived from lemongrass was treated with icing sugar (5 g, 2-4%. w/w tapioca starch) by dusting. The mixture was heated in an oven at 40° C. for 30 minutes and then the temperature was increased to 180° C. for 5 minutes. The increase in temperature caused discoloration of the icing sugar showing that the blended fibres were evenly covered with hydrophilic substance.

Those skilled in the art will appreciate that the invention described herein is susceptible to variations and modifications other than those specifically described. It is to be understood that the invention includes all such variations and modifications which fall within the spirit and scope. The invention also includes all of the steps, features, compositions and compounds referred to or indicated in this specification, individually or collectively, and any and all combinations of any two or more steps or features.

Example 5 Plywood

The composition of the present application can be used with advantage to make one or more of the layers of a layered product such as plywood. Plywood broadly describes a family of products where layers, sometimes termed veneers or plys, are glued together, sandwich-like, to form a layered composite product. These individual layers may be treated with a hydrophilic substance prior to resin application and manufacture of ply. Individual layers can be made from MDF or chipboard or, in this instance, layers manufactured from the composition described and claimed in the present application.

Further Examples Engineered Wood Products

Embodiments of the composition of the present invention may be advantageously incorporated in various engineered wood products as outlined below and are so claimed in the present application:

Engineered wood products are manufactured by gluing together ligneous softwood material to a known standard. The raw ligneous (containing wood fibre) material is sourced from all stages of timber production including thinnings, logs and mill byproducts such as dimensioned wood offcuts, woodchips and sawdust. Softwood tree species are primarily used because of their more favorable fibre and density properties compared with hardwood species. However, hardwood species are often the source of ligneous material for hardboard manufacture and veneers used in the production of plywoods.

Primary engineered wood products are made using a wide variety of technologies. Logs and wood offcuts can be pulverised, chipped or flaked and reconstituted using adhesives into sheets or wood based panels. Alternatively, wood offcuts can be joined end to end by finger jointing and gluing to form longer lengths of dimensioned lumber. Wood based panel products include medium density fibreboard (MDF), particleboard, hardboard, oriented strand board (OSB) and plywood. Load bearing products include laminated veneer lumber (LVL), glued laminated timber (glulam) and I-beams.

Medium density fibreboard is a fibreboard using reconstituted fine wood fibres. The fibres are bonded using adhesives and then heat pressed. MDF is well suited to further machining (such as routing) and a wide range of internal applications such as furniture manufacturing. Particleboard manufacture is similar to that of MDF, but uses predominantly larger chips. It is suitable for interior use only and remains the world's dominant wood based panel. Particleboard is used extensively in structural applications (floors, stairs) and in cabinet making.

Hardboard is manufactured using hardwood ligneous fibres, without additional adhesives. Under sufficient heat and pressure, lignin will flow and act as a thermosetting adhesive. In Australia hardboard is commonly recognised as Masonite™ or Weathertex™.

Plywood is made of thin sheets of veneer peeled from a log and arranged in layers to form a panel. Alternate layers are oriented at 90 degrees to enhance the strength of the panel. Glues and hot pressing are used to adhere and bond the veneer layers into a panel product. Plywood is used widely in both construction and furniture manufacturing industries.

Oriented strand board manufacture also requires adhesives, heat and pressure but consists of compressed ligneous strands arranged in layers oriented at right angles to one another, similar to plywood. OSB is widely used in commercial and residential construction and can be the vertical, load bearing component of I-beams.

Laminated veneer lumber is created by gluing layers of graded wood veneers into blocks with the grain of each layer of veneer running in the same direction. These blocks are then sawn lengthways to produce dimensioned lumber. The greater dimensional and load bearing characteristics of LVLs compared with solid lumber make them ideal for construction and spanning.

I-beams consist of top and bottom flanges united with webs. The flanges are generally made of solid sawn lumber or LVL and the webs are made from plywood or OSB. I-beams provide a strong, economical and lightweight load bearing solution in residential and light commercial applications.

Glued laminated timber (glulam) consists of solid wood laminations bonded together with strong, waterproof adhesives. Glulam provides load bearing solutions in both commercial and residential construction, particularly where requirements are for spanning of long distances or curved beams and trusses.

Adapted from: APA—The Engineered Wood Association (2004); Forest Products Laboratory (1999).

VARIATIONS

Other variations can be contemplated within the scope of this present invention.

For example miscanthus can be utilised as a fibre.

Boards may be made with very little resin, being comprised of cellulosic fibre and a hydrophilic substance such as, ascorbic acid with other additives that are commonly added such as wax ammonia and or sulphuric acid. 

1. A composite board comprising: i) cellulosic plant material; ii) a hydrophilic substance in the form of ascorbic acid and/or vitamin C; and iii) an adhesive or resin.
 2. The composite board according to claim 1 which is a particle board or fibre board.
 3. The composite board according to claim 1 wherein the cellulosic plant material comprises cellulosic material derived from a woody plant, cellulosic material derived from recovered or recycled wood, non-wood cellulosic material or mixtures thereof.
 4. The composite board according to claim 3 wherein the cellulosic plant material comprises material derived from a woody plant.
 5. The composite board according to claim 3 wherein the cellulosic plant material comprises non-wood cellulosic plant material.
 6. The composite board according to claim 5 wherein the non-wood cellulosic plant material is selected from corn stover, rice straw, wheat straw, barley straw, oat straw, rape seed straw, switch grass, siteria grass, flax, yukka fibre, lemongrass, jute, sisal, bamboo, pine needles, lupins, kenaf, coir fibre, coconut husks, cotton stalks, coffee husks, ground nut husks, areca nut husks, casaurina leaves, banana leaves and banana stem.
 7. The composite board according to claim 1 wherein the hydrophilic substance is selected from polyhydroxy compounds, polycarboxylic acids, hydroxycarboxylic acids, amino acids and hydroxyamino compounds.
 8. The composite board according to claim 7 wherein the hydrophilic substance is selected from ascorbic acid.
 9. The composite board according to claim 8 wherein the carbohydrate is selected from glyceraldehyde, erythrose, threose, ribose, arabinose, xylose, lyxose, allose, allose, glucose, mannose, gulose, idose, galactose, talose, sucrose, maltose, lactose, fructose and mixtures thereof.
 10. The composite board according to claim 8 wherein the hydrophilic substance is ascorbic acid in the form of vitamin C.
 11. The composite board according to claim 1 wherein the adhesive or resin is selected from a polyvinylacetate resin, a formaldehyde resin, a urea melamine resin, a melamine formaldehyde resin, a phenol formaldehyde resin, a phenol melamine formaldehyde resin, a melamine resin, a urea formaldehyde resin, a melamine urea formaldehyde resin, a melamine urea phenolic formaldehyde resin, a methylene diphenyl diisocyanate resin, a polymethylene diphenyl diisocyanate resin or a combination thereof.
 12. The composite board according to claim 11 wherein the adhesive or resin is selected from a melamine urea formaldehyde resin and a polymethylene diphenyl diisocyanate resin.
 13. A method of making a composite board comprising the steps of: i) providing particulate cellulosic plant material; ii) treating the cellulosic plant material with a hydrophilic substance; iii) optionally adding an adhesive or resin to the cellulosic plant material treated with the hydrophilic substance iv) forming a board with the mixture formed in step iii); and v) drying the board.
 14. The method of making a composite board according to claim 13 wherein the composite board is selected from a particle board and a fibre board.
 15. The method according to claim 13 wherein the cellulosic plant material comprises cellulosic material derived from a woody plant, cellulosic material derived from recovered or recycled wood, non-wood cellulosic material or mixtures thereof.
 16. The method according to claim 13 wherein the cellulosic plant material comprises material derived from a woody plant.
 17. The method according to claim 13, wherein the particulate cellulosic plant material has an average particle size in the range of 5 to 200 mm in length.
 18. The method according to claim 13 wherein the hydrophilic substance is added in an amount of 3 to 7% by weight of the cellulosic plant material.
 19. The method according to claim 13, wherein the resin is a melamine urea formaldehyde resin. 20-27. (canceled)
 28. The method according to claim 13 wherein the resin is a polymethylene diphenyl diisocyanate resin.
 29. The method according to claim 13 wherein the resin or adhesive is added in an amount of between 1 and 40% by weight of the cellulosic plant material.
 30. The method according to claim 13 wherein the melamine urea formaldehyde resin is added in an amount of 10 to 20% by weight of the cellulosic plant material.
 31. The method according to claim 13 wherein the polymethylene diphenyl diisocyanate resin is added in an amount of 1 to 10% by weight of the cellulosic plant material. 